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Date: Mon, 18 Sep 2017 11:11:15 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Tom Herbert <tom@...ntonium.net>, "David S. Miller" <davem@...emloft.net> Subject: [PATCH 4.12 21/52] kcm: do not attach PF_KCM sockets to avoid deadlock 4.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet <edumazet@...gle.com> [ Upstream commit 351050ecd6523374b370341cc29fe61e2201556b ] syzkaller had no problem to trigger a deadlock, attaching a KCM socket to another one (or itself). (original syzkaller report was a very confusing lockdep splat during a sendmsg()) It seems KCM claims to only support TCP, but no enforcement is done, so we might need to add additional checks. Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Signed-off-by: Eric Dumazet <edumazet@...gle.com> Reported-by: Dmitry Vyukov <dvyukov@...gle.com> Acked-by: Tom Herbert <tom@...ntonium.net> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- net/kcm/kcmsock.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -1383,6 +1383,10 @@ static int kcm_attach(struct socket *soc if (!csk) return -EINVAL; + /* We must prevent loops or risk deadlock ! */ + if (csk->sk_family == PF_KCM) + return -EOPNOTSUPP; + psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL); if (!psock) return -ENOMEM;
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